1. Field of the Invention
The present invention relates to a power supply apparatus, and more particularly, to a power supply apparatus capable of stably supplying internal power within a wide range from a minimum input voltage to a steady state of an output of a boost stage.
2. Description of the Related Art
In the case of a general AC-DC power supply apparatus, a latter stage of an AC-DC rectifying unit is mainly provided with a two-stage configuration of a power factor correction (PFC) unit and a DC-DC conversion unit. Recently, a type of implementing a single-stage in which functions of the PFC unit and the DC-DC conversion unit are integrated into one for high power density has been mainly used but has power factor and efficiency lower than those of a type of implementing a two-stage, and therefore is restrictively used in products. Further, in the two-stage configuration, as the PFC unit, a boost converter has been widely used and as the DC-DC conversion unit, a flyback converter, a full-bridge converter, and an inductor-inductor-capacitor (LLC) resonant converter have been widely used. The flyback converter has low efficiency but is advantageous in multi-output generation using a transformer, as compared with the LLC resonant converter. The full-bridge converter may not be used for products having low power density due to a larger number of devices and may have reduced efficiency at the time of a light load. For this reason, the LLC resonant converter, which may have high efficiency with a smaller number of devices, has been mainly used. However, the LLC resonant converter has a narrow input range with respect to a supply of internal power, and thus may not generate the internal power at a minimum input voltage like the flyback converter.
Meanwhile, in the two-stage power supply apparatus configured of the boost converter and the LLC resonant converter, the related art, which generates the internal power may largely include the following two methods.
The first method uses an additional standby stage at the outside. The method supplies the internal power from an output of the AC-DC rectifying unit (bridge diode) through the additional standby stage and therefore may achieve a stable operation. In this case, the standby stage generally uses the flyback converter. The method may be used in the case in which the use of the standby stage is essential and the case in which the required power density is low and may not be used due to a spatial disadvantage in the case in which the high power density is required.
The second method is a method of generating internal power from an output of the PFC unit through a regulator. The second method is a method of applying a voltage regulator to an output of a PFC unit to constantly supply internal power at all times within a wide range from a minimum input voltage to a boost steady output at least three times as large as an input voltage and may increase costs and the overall size of the apparatus since a loss of the output voltage of the PFC unit normally operated is large and the available regulator also needs to use a product having a large voltage threshold.